She’s a cat-loving Guardian reader with a secret tattoo who enjoys baking her own bread. Yet among the numerous things Sherlock instantaneously deduced about John Watson’s fiancé Mary Morstan on their first meeting, there was one he chose to ignore: Liar.
Even as John and his new wife celebrated their nuptials in episode two, there was a further clue that Mary was not exactly what she seemed.
A congratulatory telegram from “CAM” went unnoticed by Sherlock, and meant nothing to John but left Mary visibly shaken after it wished her “oodles of love and heaps of good wishes”, adding “Wish your family could have seen this..."
Now we know exactly what the orphaned Mary was hiding and what she had to fear from master blackmailer Charles Augustus Magnussen, aka CAM.
Her hazy background and limited group of friends were symptoms of a previous life in which Mary was a ruthless trained killer.
Her final throw of the dice to prevent John from finding out was an assassination attempt on the man who threatened to reveal her secret, Lars Mikkelsen’s manipulative newspaper magnate Magnussen.
Of course, Mary reckoned without the interference of her husband’s best friend. She was forced to shoot and wound Sherlock in order to protect her marriage but was eventually tricked into inadvertently confessing the truth in John's presence.
John's love for his wife – not to mention the attraction to danger that has seen him surround himself with people like Sherlock and Mary – was eventually enough to persuade him to ignore her past and focus on their future.
Sherlock fans will be doing the same – after all, a kick-ass trained assassin can only be a good addition to John and Sherlock's crime-fighting outfit...
Sherlock season 4 could come sooner than expected
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